The present invention relates to an injection timing device intended to regulate the timing of the injection of fuel into an internal combustion engine, and more particularly into a piston engine.
It is known that such an injection timing device should satisfy two main requirements. The first main requirement is control of the amount of fuel to be injected into each cylinder in each combustion cycle. The amount of fuel injected is preferably varied as a function of the desired load for the motor. The second main requirement is control of the instant in time at which the injection operation occurs in relationship to the sequence of events of each combustion cycle and as a function of the desired advance timing of the combustion cycle.
An injection timing device, called a double slide valve device, in which the high fuel pressure is provided at each of the two opposite faces of the injection needle of the fuel injector is already known. When a drop in the pressure on one face of the needle, often referred to as the rearward face of the needle, occurs due to the movement of one of the two slide valves an injection operation is initiated. In fact, the injection needle is then raised off its seat due to the high pressure which continues to prevail on the other face of the injection needle, often referred to as the forward face of the injection needle.
Moving the other slide valve causes the reestablishment of high pressure on the one face or rearward face, of the needle, which causes the reseating of the injection needle with the aid of its adjusting spring. This event corresponds to the end of the injection operation.
In this known system, each of the slide valves is driven separately by the action of fuel at a moderate pressure delivered by microvalves, themselves controlled by an electronic computer.
This known system, thus, makes it possible to control the start and the end of an injection operation, independently, by a computer. On the other hand, it is found that the variation in the opening time of the injection needle and, thus, in the delivery output, is equal to the sum of the variations in the times of opening and closing. The exact amount of fuel delivered is, thus, difficult to reproduce from one combustion cycle to another, thus, resulting in a certain irregularity in the operation of the motor.